Refractory metal alloy castings and methods of making same



Patented Dec. 25, 1951 REFRACTORY METAL ALLOY CASTIN GS AND METHODS OFMAKING SAME Frederick P. Bens, Detroit, and John L. Ham, Dearborn,Mich., and Robert M. Parke, Silver Spring, Md., assignors to ClimaxMolybdenum Company, New York, N. Y., a corporation of Delaware NoDrawing. Application September 25, 1947, Serial No. 776,166

14 Claims. (Cl. 75-476) The present invention relates to improvedrefractory metal alloy castings and methods of preparing the same.

In the past it has not been possible to produce forgeable castings ofrefractory metals such as molybdenum and tungsten. Consequently, theonly method of producing metals of this type which could be hot workedhas been to form bars of sintered, powdered material. While this methodhas been used extensively, particularly in the production of tungstenwire, it isimpractical for the production of large forgings, because ofthe difliculty of making large bodies of sintered, powdered metal. Priorattempts to melt and cast such refractory metals have resulted incastings which were exceedingly brittle and which could not be hotworked.

Accordingly, it is the principal object of the present invention toprovide a refractory metal in cast form which can be forged, swaged,rolled or drawn while hot.

Another object of the present invention is to provide a process ofproducing such castings.

In accordance with the present invention it is found that castings ofrefractory metals such as molybdenum and tungsten may be hot worked ifthey contain small quantities of carbon and the oxygen is reduced belowan exceedingly minute quantity. Thus, an alloy containing carbon from0.01 to 0.25 per cent, oxygen less than 0.005 per cent, and the balancemolybdenum or tungsten or any alloy of both, may be forged. For thispurpose a metal is considerable forgeable if its cross-sectional areamay be reduced at least fifty per cent while hot. For best results thecarbon content should lie between 0.03 and 0.10 per cent and the oxygencontent should be less than 0.003 per cent. Within this preferred range,cast ingots which may be rolled into bars, rods, or sheet, andsubstantially reduced in cross-sectional area may be obtained.

At the present time so-called commercially pure refractory metals areobtainable as powders. It is found. however, that these metal powderscontain small quantities of oxygen which must be removed in order toproduce a forgeable casting. In accordance with the present invention,this oxygen is removed from the metal by the addition, at the time ofmelting or before, of calculated quantities of carbon and the meltingoperation is carried out under a high vacuum. For this purpose thepressure in the melting chamber must be less than 500 microns of mercuryand preferably less than microns. The amount of carbon which is addedmust exceed the calculated amount necessary to combine with the quantityof oxygen present in the material by an amount sufficient to produceresidual carbon within the limits specified above. In this connection itis found that as the pressures approach the higher limit it is necessaryto employ carbon in quantities correspondingly approaching the highercarbon limit. Accordingly, the quantity of oxygen in the raw materialmust be accurately measured. For this purpose the wellknown vacuumfusion method of determining oxygen content may be employed.

While any suitable method of adding carbon to the metal and melting themixture may be employed, the preferred method is to mix the powderedrefractory metal with powdered carbon in the necessary proportions andcompact the mixture by pressure into a bar Or rod. This rod is thenheated sufiiciently, preferably by electric resistance heating, tosinter the powdered ma terials into a bar of sufiicient strength to beused as an electrode in a vacuum arc melting furnace. This bar is thenutilized as one electrode of the arc and consumed, the oppositeelectrode being preferably the bath of melted material. For this purposeit is preferred to use a water-cooled copper mold to collect the moltenmaterial. Any suitable means may be provided to support the consumableelectrode in proper spaced relation to the bath of molten metal andmaintain it in the spaced relation during the melting operation. At thestart of the melting operation a small piece of the same refractorymetal may be placed in the mold to act as the starting electrode pendingformation of the molten bath.

The interior of the mold and the entire melting chamber is suitablyenclosed and evacuated by conventional means.

It will be apparent to those skilled in the art that variations in themethod of producing forgeable refractory metal castings in accordancewith the present invention may be indulged in without departing from thespirit of the invention or the scope of the appended claims.

We claim:

1. A cast alloy containing from 0.01 to 0.25 per cent carbon, not morethan 0.005 per cent oxygen and the balance essentially all molybdenum.

2. A cast alloy containing from 0.03 to 0.10 per cent carbon, not morethan 0.003 per cent oxygen and the balance essentially all molybdenum.

3. A cast alloy characterized by its forgeability and containing from.01 to .25 per cent carbon, not more than .005 per cent oxygen and thebalance essentialh all of at least one metal selected from the groupconsisting of tungsten and molybdenum.

4. A cast alloy characterized by its forgeability and containing from.03 to .1 per cent carbon, not more than .003 per cent oxygen and thebalance essentially all of at least one metal selected from the groupconsisting of tungsten and molybdenum.

5. The process of producing a casting consisting essentially of carbonand at least one metal selected from the group consisting of molybdenumand tungsten which consists in adding to the powdered metal a calculatedquantity of carbon sufficiently in excess of that required to combinewith the oxygen in said metal to produce a residual carbon content ofbetween .01 and .25 per cent, sintering said powdered metal into a bar,melting said bar by utilizing it as an electrode in a vacuum arcfurnace, and collecting the molten metal in a mold, said melting andcollecting operations being carried out at an absolute pressure notexceeding 500 microns of mercury.

6. The process of producing a casting consisting essentially of carbonand at least one metal selected from the group consisting of molybdenumand tungsten which consists in adding to the powdered metal a calculatedquantity of carbon sufficiently in excess of that required to combinewith the oxygen in said metal to produce a residual carbon content ofbetween .01 and .25 per cent, sintering said powdered metal into a bar,melting said bar by utilizing it as an electrode in a vacuum-arcfurnace, and collecting the molten metal in a mold, said melting andcollecting operations being carried out at an absolute pressure notexceeding 100 microns of mercury.

'7. The process of producing a casting consisting essentially of carbonand molybdenum which consists in adding to the powdered metal acalculated quantity of carbon suiiiciently in excess of that required tocombine with the oxygen in said metal to produce a residual carboncontent of between .01 and .25 per cent, sintering said powdered metalinto a bar, melting said bar by utilizing it as an electrode in a vacuumarc furnace, and collecting the molten metal in a mold, said melting andcollecting operations being carried out at an absolute pressure notexceeding 100 microns of mercury.

8. The process of producing a casting consisting essentially of carbonand molybdenum which consists in adding to the powdered metal acalculated quantity of carbon sufficiently in excess of that required tocombine with the oxygen in said metal to produce a residual carboncontent of between .03 and .10 per cent, sintering said powdered metalinto a bar, melting said bar by 4 utilizing it as an electrode in avacuum arc furnace, and collecting the molten metal in a mold, saidmelting and collecting operations being carried out at an absolutepressure not exceeding 100 microns of mercury.

9. The process of producing a casting consisting essentially of carbonand at least one metal selected from the group consisting of molybdenumand tungsten which consists in adding to the metal a calculated quantityof carbon sufficiently in excess of that required to combine with theoxygen in said metal to produce a residual carbon content of between .01and .25 per cent and melting said mixture and collecting the moltenmetal in a mold, said melting and collecting operations being carriedout at an absolute pressure not exceeding 500 microns of mercury.

10. The process of producing a casting consisting essentially of carbonand at least one metal selected from the group consisting of molybdenumand tungsten which consists in adding to the metal a calculated quantityof carbon sufliciently in excess of that required to combine with theoxygen in said metal to produce a residual carbon content of between .03and .10 per cent and melting said mixture and collecting the moltenmetal in a mold, said melting and collecting operations being carriedout at an absolute pressure not exceeding microns of mercury.

11. The process of producing a casting consisting essentially of carbonand molybdenum which consists in adding to the metal a calculatedquantity of carbon sufliciently in excess of that required to combinewith the oxygen in said metal to produce a residual carbon content ofbetween .01 and .25 per cent and melting said mixture and collecting themolten metal in a mold, said melting and collecting operations beingcarried out at an absolute pressure not exceeding 500 microns ofmercury.

12. The process of producing a casting consisting essentially of carbonand molybdenum tungsten which consists in adding to the metal acalculated quantity of carbon sufiiciently in excess of that required tocombine with the oxygen in said metal to produce a residual carboncontent of between .03 and .10 per cent and melting said mixture andcollecting the molten metal in a mold, said melting and collectingoperations being carried out at an absolute pressure not exceeding 100microns of mercury.

13. The process of producing a casting consisting essentially of carbonand molybdenum which consists in adding to the powdered metal acalculated quantity of carbon sufiiciently in excess of that required tocombine with the oxygen in said metal to produce a residual carboncontent of between .01 and .25 per cent, sintering said powdered metalinto a bar, melting said bar by utilizing it as an electrode in a vacuumarc furnace, and collecting the molten metal in a mold, said melting andcollecting operations being carried out at an absolute pressure notexceeding 500 microns of mercury.

14. The process of producing a casting consisting essentially of carbonand molybdenum which consists in adding to the powdered metal acalculated quantity of carbon sufliciently in excess of that required tocombine with the oxygen in said metal to produce a residual carboncontent of between .03 and .10 per cent, sintering said powdered metalinto a bar, melting said bar by utilizing it as an electrode in a vacuumarc furnace, and collecting the molten metal in a mold,- said meltingand collecting op- 5. 6 erations being carried out at an absolute pres-Number Name Date, sure not exceeding 500 microns of mercury. 1,658,712Fonda Feb. 7, 1928 FREDERICK P. BENS. 1,731,267 Rich Oct. 15, 1929 JOHNL. HAM. 1,830,200 Hidnert Oct. 4, 1932 ROBERT M. PARKE. 5 2,040,566 RohnMay 12, 1936 2,277,211 Cooper Mar. 24, 1942 REFERENCES CITED N bFOREIGI: PATENTS t The following references are of record in the um erConn ry 6 me of this, patent: m 338,409 Great Britain Nov. 20, 1930UNITED STATES PATENTS OTHER REFERENCES Parke et a1.: Treatise in MetalsTechnology, Number Name Date Sept. 1946, Tech. Pub. No. 2052, 12 pages,pub.

1,365,091 Clement Jan. 11, 1921 b I t m 1 5 2 Lehmann 6' 1 7 15 y m 11$M 11 8 Met- EngrS-. New YOlk-

3. A CAST ALLOY CHARACTERIZED BY ITS FORGEABILITY AND CONTAINING FROM.01 TO .25 PER CENT CARBON, NOT MORE THEN .005 PER CENT OXYGEN AND THEBALANCE ESSENTIALLY ALL OF AT LEAST ONE METAL SELECTED FROM THE GROUPCONSISTING OF TUNGSTEN AND MOLYBDENUM.